The present invention relates to a workpiece transporting apparatus in general, and more particularly to an apparatus for gripping an elongated workpiece and transporting it out of a machine tool.
Apparatus of this general type are already known in the art, for example from German Pat. No. 906,924 or from Gebrauchsmuster No. 734,164. They serve to withdraw elongated workpieces, for example rods, bars or the like, from drawing benches or turning lathes.
In order to obtain high and uniform withdrawing speeds as a workpiece is being withdrawn from a machine tool, such as a drawing bench or the like, it is necessary to utilize several gripping devices which grip the workpiece and withdraw it and which engage the workpiece in succession. However, during disengagement of one gripping device and engagement by the next one, special problems which heretofore have caused difficulties. Due to the change of the locus at which the gripping and withdrawing force acts upon the workpiece as one gripping device disengages the workpiece and another one engages it, the withdrawing speed, i.e., the speed at which the workpiece is withdrawn from the machine tool and is transported out of the same, is temporarily decreased. An additional negative effect results at the same time in that the workpiece tends to slip, approximately analogous to the release of a tensioned rubber cord, as the clamping jaws of one device disengage and before the clamping jaws of the next device have properly engaged the workpiece. This causes the clamping jaws to leave scraping marks on the workpiece which is undesirable. This problem occurs even if the releasing gripping device and the next-engaging gripping device are both driven by one and the same drive.
All of these problems are aggravated by the fact that demands are made for increased transporting and withdrawing speeds, and that these increased speeds require increased speeds of the gripping devices that must move to and fro in order to alternately engage and release the workpiece. This requires more and more complicated constructions that ultimately become too expensive to become economically feasible. From a certain withdrawing speed on, therefore, gripping devices which shuttle to and fro are no longer practical.